I know, I too quibbled about his birth before sending you this information. Actually, his sister Luce was born in Cheticamp Nov 1838, and a brother Pierre-Eusebe also there in Dec 1839. Your Urbain is the second of that name, another Urbain was born at the Magdalens in Sep 1842, but must have died young, as your Urbain was named the same although born in 1844. Back in those times, people didn't actually remember when they were born (if illiterate). Ages weren't important to them as well. He could well have picked a birthdate and stuck to it in several of the records you have seen.
In any event, this is the closest one I could find, whose family situation of moving to Newfoundland fit. As I said in my post, this could "possibly" be him. There weren't that many Poiriers who settled in Newfoundland. You could also write to/e-mail the Société St-Pierre (they speak English) in Cheticamp and see if they have another one that may be closer in age/year to yours. Their e-mail is
genealogie.cheticamp@lestroispignons.comAs for Miquelon, there are a bunch of years missing at the French Overseas archives, including 1839, but I doubt his birth being there as I have never seen an Urbain Poirier born there in any censuses close to that time.